Oxidation dyes are formed when a developer component couples with a coupler component under oxidative conditions. These oxidative dyes are preferred in dyeing human hair since they produce intense color and usually possess satisfactory fastness.
Good oxidation hair dyes must meet the following requirements:
They must form by oxidative coupling of respective developer-coupler combinations the desired color tones of sufficient intensity. The dyes must also have good substantivity on human hair, and should be toxicologically and dermatologically safe.
Couplers which are known in oxidative dye systems include derivatives of m-phenylene diamine, phenols, naphthols, derivatives of resorcinal and pyrazolones. Well known developers such as p-phenylenediamine derivatives, diaminopyridines, 4-amino-pyrazolone and heterocyclic hydrazones are generally used in oxidation dye systems.
Oxidation dyes for hair are supplied in many cosmetic forms such as creams, emulsions, gels, or simple solutions. These are obtained in a conventional manner by mixing the coupler and developer with the usual vehicles and aids. Among these components are wetting agents and emulsifiers of the anionic and non-ionic type such as alkylbenzene sulfonates, fatty alcohol sulfates, alkyl sulfonates, fatty acid alkanolamides and the addition products of ethylene oxide and fatty alcohols; thickeners such as methyl cellulose, starch, higher fatty alcohols. Other ingredients which may also be included would be paraffin oils, fatty acids, perfumes and hair conditioners such as pantothenic acid or cholesterol.
The oxidative coupling of the oxidation dye components can occur by simple exposure to atmospheric oxygen. This is a slow process so as a rule chemical oxidizing agents are used. Hydrogen peroxide or its addition products with urea, melamine or sodium borate are commonly used.